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The mechanism of Cu2+ loading into commercially available natural HEU‐type and synthetic LTA‐type zeolites for their possible use in environmental processes, such as water and air treatment applications, was studied. Elemental analysis, SEM/EDXS, XRD, XAS and XPS analyses revealed 4‐fold coordination of Cu2+ cations with oxygen atoms in the pores, a predominant location of copper atoms on the surface of crystallites and retained crystallinity of zeolites throughout the processes. The post‐treatment of Cu2+‐loaded samples with HCl and/or NaCl solutions confirmed the predominantly reversible sorption of copper on zeolites from aqueous solutions by ion‐exchange mechanism and, therefore, excellent regeneration possibilities for both types of zeolites. Furthermore, with the calcination of exhaust metal‐loaded zeolites, catalysts for total toluene oxidation reaction, as a model VOC pollutant, were obtained. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this research is to examine how Cu modification can improve the photocatalytic activity of TiO2‐SiO2, to explain the correlation between the Cu concentration and the chemical state of Cu cations in the TiO2‐SiO2 matrix, and the photocatalytic activity under UV/solar irradiation. The Cu‐modified TiO2‐SiO2 photocatalysts were prepared by a low‐temperature sol–gel method from organic Cu, Si and Ti precursors with various Cu concentrations (0.05–3 mol %). The sol–gels were dried at 150 °C to obtain the photocatalysts in a powder form. The photocatalytic activity was determined by using a fluorescence‐based method of terephthalic acid decomposition. An up to three times increase in photocatalytic activity is obtained if the TiO2‐SiO2 matrix is modified with Cu in a narrow concentration range from 0.05 to 0.1 mol %. At higher Cu loadings, the photocatalytic activity of the Cu‐modified photocatalysts is lower than that of the un‐modified reference TiO2‐SiO2 photocatalyst. XRD was used to show that all Cu‐modified TiO2‐SiO2 composites with different Cu concentrations have the same crystalline structure as un‐modified TiO2‐SiO2 composites. The addition of Cu does not change the relative ratio between the anatase and brookite phases or unit cell parameters of the two TiO2 crystalline structures. We used Cu K‐edge X‐ray absorption near edge structure and extended X‐ray absorption fine structure analyses to determine the valence state and local structure of Cu cations in the Cu‐modified TiO2‐SiO2 photocatalysts. The results elucidate the mechanism responsible for the improved photocatalytic activity. In samples with a low Cu content, which exhibit the highest activity, Cu−O−Ti connections are formed, which suggests that the activity enhancement is caused by the attachment of CuII cations on the surface of the photocatalytically active TiO2 nanoparticles, so CuII cations may act as free‐electron traps, which reduce the intensity of recombination between electrons and holes at the TiO2 photocatalyst surface. At higher Cu loadings no additional Cu−O−Ti connections are formed, instead only Cu−O−Cu connections are established. This indicates the formation of amorphous or nanocrystalline copper oxide, which hinders the photocatalytic activity of TiO2. [ABSTRACT FROM AUTHOR]

The development of efficient TiO2-based photocatalysts for water treatment is mainly performed by doping with transition metals or by establishing junctions between different phases, metal-semiconductor or semiconductor-semiconductor. We present, for the first time, the synthesis of Zr- and Mn-modified TiO2 by a redesigned sol-gel technique that allows the formation of heterometallic bridges on the TiO2 surface. Cations of the doping metals are located in the pores of mesoporous anatase and attached to the crystalline TiO2 walls. The presence of the Zr enhances the photoactivity of the TiO2 catalyst. However, the introduction of Mn decreases the photocatalytic efficiency in a nonadditive manner. The inhibition effect was assigned to the side reaction between hydroxyl radicals and Mn ions. The fact that Mn effectively scavenges the hydroxyl radicals and, consequently, inhibits the whole oxidation process is direct proof that hydroxyl radicals are the main reactive species in the photocatalytic oxidative processes on TiO2 surfaces in aqueous media and the process of .OH generation is the rate-determining step, which was confirmed using a method based on the decolorization of a commercial dye Bezaktiv Blau in a reaction with Fenton's reagent as a source of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between hexavalent chromium Cr(VI), as K2CrO4, and standard humic acids (HAs) in bulk solution was studied using three complementary analytical methods: UV-Visible spectroscopy, X-ray absorption spectroscopy and differential pulse stripping voltammetry. The observed UV-Vis and X-ray absorption spectra showed that, under our experimental conditions, HAs did not induce reduction of Cr(VI) to its trivalent chemical form. The interaction between Cr(VI) and HAs has rather led to the formation of Cr(VI)–HAs micelles via supramolecular chemical processes. The reported results could contribute towards explaining the relative persistence of ecotoxic hexavalent chromium in soils. [Copyright &y& Elsevier]

This paper investigates the structural and magnetic properties of a mixed series of ferrites having general formula Co 0.5 Zn 0.25 M 0.25 Fe 2 O 4 (M = Ni, Cu, Mn, Mg). Insights on surface chemistry, structural and morphological parameters are presented in order to achieve highly tuned ferrite systems with specific characteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRD and Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations for all the samples. Co cations occupied the octahedral sites in proportion of 100% for Co–Zn–Cu, Co–Zn–Mg and around 80% for Co–Zn–Ni, Co–Zn–Mn. Ni cations were found only in the octahedral sites, while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution results were correlated with the magnetic properties data. At the same time, not only the cation distribution, but also the particles size distribution was observed to have a great influence on magnetic and optical properties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FT-IR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover, the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states (Mn2+and Mn4+) was elucidated. Finally, parallels have been drawn between the use of different cations in mixed ferrites in order to gain specific properties. • Synthesis of novel mixed ferrites Co–Zn-M (M = Ni, Cu, Mn, Mg) is described. • Surface characterization techniques confirm the functionalization with organic groups. • X-ray absorption spectroscopy results revealed a peculiar behavior of Mn containing ferrite. • Magnetic properties as function of particles size and cation distribution are summarized. [ABSTRACT FROM AUTHOR]

Triclinic ZnAPO-34 and triclinic FAPO-34 were synthesized by hydrothermal crystallization from zinc(II)- and iron(II)-containing gels. The products are thermally stable up to 900 °C. XANES and EXAFS analyses were applied to study the local environment of zinc in the ZnAPO-34 samples, while XANES analysis and Mo¨ssbauer spectroscopy were performed on the iron-substituted samples. Zn(II) remains in the same oxidation state during synthesis and after thermal treatment, while iron exhibits Fe(II) and Fe(III) oxidation states. Analysis of the local structure showed that Zn(II) is located on tetrahedral sites of the framework, while Fe(II) and Fe(III) are present on octahedral sites. Infrared study of carbon monoxide adsorption at 100 K showed the presence of strong Brønsted acid sites on the Zn and Fe(II) samples, indicating the substitution of the metals in the framework. Rhombohedral FAPO-34 can be reversibly oxidized in the infrared cell, evidencing the disappearance of the Brønsted acid sites in the Fe(III) oxidation state. [Copyright &y& Elsevier]